1. Field of the Invention
The present invention relates to a lenticular lens having a large number of lens elements defined so that their ridges are aligned in parallel with each other. The present invention also relates to a surface light source having the lenticular lens, and a liquid crystal display apparatus having the surface, light source as a back-light thereof.
2. Information of the Related Art
As disclosed in Japanese Patent Laid-Open Publication No. 2-284102 and 63-318003, and Japanese Utility Model Laid-Open Publication No. 3-92601, and the like, liquid crystal display apparatuses having a back-light type diffusing surface light source or edge-light type diffusing surface light source are known. Such surface light sources have a lenticular lens formed of a large number of triangular prism shaped lens elements which are defined in such a way that their edges are aligned in parallel. The lenticular lens equally and isotopically diffuses emitted light in a desired angle range.
When a lenticular lens is used along with a delustered transparent diffusing plate (delustered transparent sheet), light energy of the light source is more sharply distributed in a predetermined angle range than when the delustered transparent diffusing plate is used alone. In addition, the light is equally and isotopically diffused in the predetermined angle range.
However, since the vertical angles .alpha. of the lens elements of the lenticular lenses are 60.degree. or 90.degree., a part of rays of light deviate from the predetermined angle range. In other words, side lobes take place in an angle distribution of the intensity of transmitted light.
Thus, such lenticular lenses are not suitable for liquid crystal display apparatuses. Although the lenticular lenses have an advantage of low power consumption, they display clear images especially in color with difficulty.
If the output of the light source were increased so as to solve such a problem, the temperature of the liquid crystal device would adversely rise. The light which leaks out of the predetermined angle range would become noise (stray light), which would disturb the viewing of the user.